1. Field of the Invention
The present invention generally relates to respiratory imaging techniques used in radiotherapy and, in particular, to techniques for using audio-visual biofeedback to improve accuracy.
2. Background Description
Respiratory motion creates several problems for thoracic radiology. It degrades anatomic position reproducibility during imaging. It necessitates larger margins during radiotherapy planning. And it causes errors during radiation delivery.
In a PHD thesis entitled “Investigating the impact of audio instruction and audio-visual biofeedback for lung cancer radiation therapy” (Virginia Commonwealth University, 2005), Rohini George describes a twenty-four patient study conducted at Virginia Commonwealth University. The study demonstrated the improvement in respiratory reproducibility and therefore image quality and radiotherapy treatment accuracy that can be obtained with audio-visual biofeedback. This study used the output of the Varian RPM (Real-time Position Management) respiratory gating system for the audio-visual biofeedback.
Operation of the Varian system is shown in FIG. 1. A patient 110 lies in a prone position, viewing a TV screen 120. The TV screen has a built-in speaker (not shown) used during the audio instructions and the audio-visual biofeedback. A marker block 130 is placed on the patient's abdomen between the umbilicus and the xyphoid, allowing measurement of the current position of the patient's breathing. In the Varian system, the image 122 presented to the patient 110 on screen 120 shows guides for the maximum 124 and minimum 126 extent of breathing, thereby allowing the patient to observe current position 128 in relation to these upper 124 and lower 126 limits. The respiratory signal 128 obtained is the anterior-posterior motion of the marker block 130.